The mechanism(s) underlying how mutations in emerin, an inner nuclear envelope protein, cause muscle disease remain unknown. Mutations in emerin cause Emery-Dreifuss muscular dystrophy (EDMD), an inherited disorder characterized by progressive skeletal muscle wasting, irregular heart rhythms, and major tendon contractures. Skeletal muscle wasting is predicted to be caused by the failure to regenerate skeletal muscle. Proper differentiation of skeletal muscle stem cells during regeneration requires the coordinated temporal expression of differentiation genes. The mechanisms underlying how mutations in emerin impair myogenic differentiation remain poorly understood. Genomic architecture controls gene activation or repression by regulating the association of the genome with transcriptionally active or repressed nuclear domains. The genome is dynamically reorganized during stem cell differentiation to coordinate the temporal expression of the differentiation transcriptional program. The field lacks a fundamental understanding of the mechanisms regulating nuclear lamina regulation of genomic architecture and its affect on gene expression. Although the nuclear lamina regulates genomic organization and chromatin architecture, lamins are not required for repressed chromatin localization at the nuclear periphery. Thus, other nuclear envelope proteins mediate their association. We hypothesize emerin is one of these proteins, since emerin interacts with repressive chromatin machinery and dynamically interacts with myogenic differentiation gene loci during differentiation; repressed loci localization is emerin-dependent. The research proposed here will examine how emerin regulates genomic organization during myogenic differentiation to coordinate the differentiation transcriptional program and how this genomic reorganization is altered in EDMD. The functional interaction between emerin and HDAC3 is predicted to recruit histone methyltransferases (HMTs) to these repressed genomic regions at the nuclear lamina to stabilize chromatin repression by an undefined mechanism. These studies are designed to begin elucidating this mechanism. Mutations in emerin are predicted to cause impaired differentiation by disrupting genomic reorganization and temporal expression of the differentiation program. These studies are also designed to define genomic regions associating with emerin and delineate how these regions change during differentiation, how this association is altered during EDMD mutant myogenic progenitor differentiation, and identify molecular pathways implicated in their impaired differentiation. These molecular pathways are potential therapeutic targets for treatment of EDMD. Future studies beyond the scope of this proposal would test small molecule activators or inhibitors of these pathways in X-EDMD mouse models and patient myoblasts.